The present invention relates to a charged particle apparatus having a combination of a focused ion beam apparatus FIB (Focused Ion Beam) and a scanning electron microscope SEM (Scanning Electron Microscope). This is often used for defect observation on a semiconductor device.
Conventionally a charged particle apparatus combined with FIB and SEM has been disclosed in a publication of JP-A-2-123749. In FIG. 3, which shows the conventional apparatus, there are provided a focused ion beam irradiating lens barrel 1 for irradiating while scanning a focused ion beam 11 vertically to a sample surface and an electron beam irradiating lens barrel 2 for obliquely irradiating by scanning a focused electron beam 12 to a focused ion beam 11 scan-irradiating position of a sample 3. Secondary charged particles produced from the sample 3 surface in response to irradiation by the focused ion beam 11 are detected by a not-shown secondary charged particle detector. Based on the detection intensity, a sample 3 surface image is displayed on a not-shown CRT. Also, based on the sample 3 surface image displayed on the CRT, a scanning region of the focused ion beam 11 can be set to etch-remove a predetermined region of the sample 3 surface. That is, a sample section can be formed at a predetermined position of the sample 3 by repeatedly scanning/irradiating the focused ion beam 11.
A focused electron beam 12 from an electron beam irradiating lens barrel 2 is irradiated while scanning to a sample 3 section formed by the focused ion beam 11. Secondary particles produced from the sample section by irradiating the electron beam 12 are detected by a secondary charged particle detector 6. A sample section image is displayed on the CRT based on the detection intensity.
The secondary ray produced from the sample section due to the electron beam 12 irradiation is not limited to secondary charged particles such as secondary electrons but includes X-ray emission. By detecting an inherent or characteristic X-ray included in the emitted X ray, the sectional portion can be analyzed based on the ingredients or composition of the sample.
Generally, the lens for focusing an ion beam uses an electrostatic lens. A scanning electrode is used for applying an electric field perpendicular to a focused ion beam optical axis in order to scan a focused ion beam 11.
Also, generally, as for the electron beam 12, an electromagnetic coil is used to focus or deflection-scan by a magnetic field.
Generally, focused ion beam 11 irradiation and electron beam 12 irradiation are alternately operated with repetition.
After operating the electron beam 12 from the electron beam irradiating lens barrel 2, even if the irradiation of the electron beam 12 is stopped to render 0 a current flowing through the electromagnetic coil, the magnetic field for focusing and scanning the electron beam 12 caused by the electromagnetic coil is not completely reduced to 0 and some residual magnetic field remains. The remaining magnetic field is not always constant due to its operation hysteresis and is sometimes varying. Due to this, if a focused ion beam 11 from the focused ion beam irradiating lens barrel 1 is operated, the focused ion beam 11 is varied in path due to the remaining magnetic field. That is, not only the position of an observed image changes in each observation but also the forming region differs from a desired region. Also, the ions forming the focused ion beam 11 are generally formed by those with a different charge ratio. For example, ions of 1 valence, 2 valences and cluster ions. Due to this different charge ratio, the amount of deflection differs. Accordingly, the focused ion beam 11 apparently spreads. That is, there is a lowering in resolving power for the focused ion beam apparatus.
Also, the secondary charged particle detector 6 has an electric field formed at a secondary electron intake port in order to introduce the secondary charged particles produced from the sample 3 surface to the secondary charged particle detector. The electric field present at the secondary charged particle detector 6 causes unwanted deflection of the electron beam 12. Particularly, if the acceleration voltage for the electron beam 12 is switched, the amount of deflection (the amount the path is deflected) of the electron beam 12 differs to vary the position at which the electron beam 12 irradiates the sample. That is, even if the focused ion beam 11 irradiating position on the sample surface and the electron beam 12 irradiating position are brought into coincidence, when the acceleration voltage for the electron beam 11 is switched, deviation occurs in these positions. In particular, in the charged particle apparatus combined with FIB and SEM, there are many things arranged close to the sample 3 and the distance between the electron beam irradiating lens barrel 2 tip and the sample (working distance) increases. Accordingly, there is an increase in the deflection amount of the electron beam 12 due to the magnetic field from the secondary electron detector.
A magnetism preventive cylinder for shielding magnetism is provided at a tip of a focused ion beam irradiating lens barrel used to irradiate and scan a focused ion beam to a sample surface. Also, an electricity preventive cylinder for shielding an electric field is arranged at a tip of an electron beam irradiating lens barrel used to irradiate the sample surface.
On a focused ion beam path, the gap between the focused ion beam irradiating lens barrel tip and the sample surface is close to the electron beam irradiating lens barrel, so that a magnetic field from an electromagnetic coil of the electron beam irradiating lens barrel can adversely affect the path of the focused ion beam. The provision of the magnetism preventive cylinder at the focused ion beam irradiating lens barrel tip places at all times the focused ion beam irradiation position constant without being affected by residual magnetism. Also, there occurs no spread in the focused ion beam due to ion valence, thereby obtaining a microscopic spot and enhancing resolving power.
Furthermore, on the electron beam path, the gap between the electron beam irradiating lens barrel tip and the sample exposes the electron beam close to the secondary charged particle detector so that the electron beam path is adversely affected by the electric field for introducing the second charged particles of the secondary charged particle detector. The provision of the electricity preventive cylinder at the electron beam irradiating lens barrel tip decreases an exposure amount thereby reducing the electron beam deflection caused by the secondary charged particle detector. Even if the acceleration voltage for the electron beam is switched, the variation amount in the electron beam irradiation position is decreased.